The Obama administration as early as Monday is expected to unveil new rules that would slash carbon emissions at existing power plants, a plan likely to drum up plenty of political controversy and become an issue in the fall congressional elections.

The rules appear to take special aim at coal and potentially could result in the closure of a large number of plants over the next decade.

Opponents are already lining up. The U.S. Chamber of Commerce argued in a new report last week that a major EPA rewrite of pollution laws would kill thousands of U.S. jobs, raise electricity prices and cost the economy up to $50 billion a year.

The debate is sure to intensify as the November elections draw near, especially in states that are heavy producer or users of coal, such as Kentucky, West Virginia, Missouri and Ohio. Critics are lambasting what they call a “war on coal” and trying to divide Democrats.

Vulnerable Democrats such as Sen. Mary Landrieu of Louisiana have already criticized the Obama administration or asked the White House to delay the rules.

Is the chamber estimate believable? No one really knows, but business groups have repeatedly exaggerated the effects of environmental and other regulations in the past.

Groups that back the new Obama administration goals, meanwhile, argue they will make the U.S. more energy efficient, cut household energy costs and even create thousands of new jobs. Yet those predictions are probably just as iffy as the Chamber’s dire warnings.

The new rules written by the Environmental Protection Agency reportedly would seek to reduce the percentage of U.S. electricity generated by coal to 14% by 2030 from about 37% right now. Coal is the single biggest source of electricity generation in the U.S. and has been for more than 60 years.

The amount of electricity generated by natural gas – a cleaner fuel than coal – would rise to 46% by 2030 from about 30% now under the EPA plan. That would make it the biggest generator of the nation’s electricity.

How soon is that likely to happen? And should investors avoid publicly traded coal companies or energy producers reliant on coal?

An analysis by Morgan Stanley says the new rules probably won’t go into effect for another four years at least. Lawsuits and other opposition could delay the rules from taking effect until 2018 at the earliest – and perhaps not at all if Republicans capture the White House in 2016.

To achieve Obama’s carbon emissions goals, Morgan Stanley analysts wrote, the EPA will need to make a broader interpretation of the Clean Air Act. “This broader approach would, in our view, invite a significant amount of litigation,” they say.

In 2009, Obama called for a 17% reduction in emissions from 2005 levels by 2020 as part of an effort to combat global warming. If what Obama proposes isn’t much above that target, the industry itself might not feel much of a bite. As the Morgan report points out, lower coal-plant output has already cut U.S. power-sector carbon dioxide emissions by about 11% in the 2005 to 2011 period.

Perhaps the bigger danger is that the new emphasis on natural gas at the expense of coal could make the U.S. too dependent on a single source of energy whose supply is uncertain. That could make the nation vulnerable to spiraling prices if natural-gas supplies declined or were disrupted.

For now the U.S. is operating on the assumption that huge shale oil and gas reserves will make the country a natural-gas powerhouse for decades to come. Yet the shale revolution is still in its early stages and estimates of recoverable reserves are still in flux. Federal authorities, for example, reportedly will soon slash their estimate of reserves in the large Monterey formation in California by a whopping 96%.

The government’s track record on energy policy has sometimes proven shortsighted or unrealistic.

In 1978, for instance, Congress passed the Industrial Fuel Use Act that banned the use of natural gas as a fuel for new power plants, owing to a perceived shortage – itself a problem caused by faulty government regulation.

The result was to spur the construction of more coal-fired plants and to boost coal usage to modern record highs until the repeal of the law a decade later.